Indicator light and control circuit



Sept? 965 R. c. CURTIS 3,205,315

INDICATOR LIGHT AND CONTROL CIRCUIT Filed May 21, 1962 ATTORNE Y8 UnitedStates Patent 3,205,315 INDICATOR LIGHT AND CONTROL CIRCUIT Roger C.Curtis, New Haven, Conn., assignor to Dictaphone Corporation,Bridgeport, Conn., a corporation of Connecticut Filed May 21, 1962, Ser.No. 196,187 3 Claims. (Cl. 179100.1)

This invention relates to an improved and simplified indicator light andcontrol circuit for a dictating machine and the like.

An object of the invention is to provide an arrangement of this kindwhich is efiective in operation, yet low in cost.

In a dictating machine, such as the one disclosed in US. Serial No.728,646 now Patent No. 3,056,606, there is an indicator light on thefront panel of the machine which lights when the machine is turned on,the sole function of this light being to distinguish between the on andthe off conditions of the machine. There is also another light alongsidethe first and whose brightness varies in accordance with signal levelduring recording. This second light glows more brightly when the soundbeing recorded increases, and less brightly, or not at all, when thesignal level decreases. Because the second light does not glow, at leastto any appreciable extent, when the machine is on but not in use, it isof course necessary in this prior arrangement to have the first lightalso. The present invention in one of its aspects provides a singlelight which is connected in a unique circuit to operate effectively as acombined on-olf, and volume level indicator.

The dictating machine described in the above-mentioned application isturned on by a switch on the machine. Thereafter, it is set inoperation, either to record or to play back, by an internal clutch whichis remotely controlled through a push-button switch mounted on a handmicrophone. The present invention in another of its aspects provides animproved circuit for controlling a clutch of this kind andsimultaneously for reacting upon the indicator light circuit to insuremaximum brightness of the light when the machine is on but not inoperation.

The clutch control circuit provided according to the invention includesan amplifying transistor, the input of which is controlled by theremotely located push-buttton switch. When this switch is closed, outputcurrent from the transistor is applied to a solenoid which actuates aclutch inside the machine and sets it into operation. An importantfeature of this arrangement is that during the initial part of turningon, the transistor applies to the clutch solenoid a large pulse ofcurrent to actuate the clutch surely and quickly. Thereafter, thecurrent ap plied is automatically lowered to a much smaller value whichis just sufiicient to keep the solenoid actuated.

The indicator light in this new arrangement comprises a single,miniature incandescent bulb or lamp which is connected in the outputcircuit of a control transistor. The input of this transistor is in turnconnected to the audio amplifier of the machine, the connection beingsuch that when there is no audio signal, the indicator light glows itsbrightest, and when there is maximum audio signal, the lamp glowsdimmest (or not at all). Now, to insure that this lamp also provides areliable indicator that the machine is turned on, a muting transistor isconnected to the audio amplifier. This muting transistor is operated bythe remote push-button switch, and when the machine is on but not inoperation this switch is open. The muting transistor is biased toconduct, thus disabling the audio amplifier. This prevents any audiosignal from reaching the control transistor to which is connected theindicator lamp. Accordingly, in this condition the lamp 3,205,315Patented Sept. 7, 1965 glows its brightest. When the machine is set inoperation, a muting transistor is biased off, thereby permitting theamplifier to work in normal fashion.

A better understanding of the invention together with a fullerappreciation of its many advantages will best be gained from thefollowing description given in connection with the accompanying drawingwhich shows a circuit embodying features of the invention.

The circuit 10 shown in the drawing includes a conventional audiopro-amplifier 12 having an input 14 adapted to receive signals from amicrophone (not shown), for example. The output of this unit 12 is fedvia a lead 16 to the input of a transistorized amplifier circuit,generally indicated at 18, which for the most part is conventional. Thiscircuit includes a driver transistor 20 and a pair of output transistors22 and 24 operated in push-pull relationship. The latter in turn appliesthrough a coupling capacitor 26 an amplified audio signal to a recordinghead, generally indicated at 28. Alternatively, as indicated by thedotted lines, when the circuit is conditioned for playback a loudspeaker30 is driven instead of the recording head.

Also connected to output transistors 22 and 24 through capacitor 26 anda second capacitor 32 is a control transistor 34. Placed in theemitter-collector circuit of the latter in series with a small valueresistor 36 is a combined indicator and volume-level lamp 38. This lamp,as previously mentioned, is placed in the front panel of a dictatingmachine, or the like where it is easily visible. When no audio signal isbeing applied to control transistor 34, lamp 38 will shine with maximumbrightness. Conversely, with maximum audio signal, the lamp will bedimmest.

T o mute amplifier circuit 18, and to prevent audio signals from beingapplied to the control transistor except when desired, i.e. duringrecording, input lead 16 is bypassed to ground by a muting transistor40. When conducting, this transistor acts as a short-circuit across theinput to transistor 20. When not conducting, muting transistor iseffectively an open circuit and transistor 20 can receive audio signalsfrom pro-amplifier 12.

The control of muting transistor is effected through a lead 42 and aresistor 44 whose lower end is adapted to be grounded through a switch46. The latter is, for example, a push-button switch mounted on a handmicrophone of a dictating machine and by which the machine is set torecord. When switch 46 is closed, lead 42 will have its biasing voltagelowered, thus increasing the effective resistance of transistor 40 to apoint where it no longer has any effect on the amplifier circuit.Simultaneously, switch 46 turns on an amplifying or switching transistor48. The latter, or a brief interval, determined by the time constant ofa capacitor 50 and resistors 52 and 54, serves as a low resistance pathfrom the positive voltage lead (-1-) to a clutch solenoid coil 56 whoselower end is now grounded by switch 46. After a short time, even thoughswitch 46 remains closed, transistor 48 will turn off leaving coil 56connected to the positive lead by a resistor 58. The value of thisresistor is such that the clutch solenoid will remain properly energizedwith minimum circuit until switch 46 is again opened. When the switch isopened, coil 56 of course will be de-energized. Also, the voltage onlead 42 will become more positive thereby making muting transistor 40very low in resistance. In this condition, though the drive motor of thedictating machine is running, the machine will not be recording andindicator light 38 will shine brightly.

The above description is intended in illustration and not in limitationof the invention. Various minor changes or modifications in theembodiments set forth may occur to those skilled in the art and thesecan be made without departing from the spirit or scope of the inventionas set forth.

I claim:

1. In a dictating machine having means for amplifying electrical voicesignals input to said machine, an indicator lamp, means for causing saidlamp to burn with a relatively high initial intensity when saidamplifying means supplies no output signal, and when an output signal issupplied by said amplifying means, to burn with an intensity lower thansaid initial intensity by an amount dependent upon the magnitude of saidoutput signal, a solenoid-operated drive clutch, and means forenergizing the solenoid of said clutch, the improvement of means fordisabling said amplifying means and thereby causing said lamp to burnwith said high initial intensity when said solenoid is not energized,said solenoid energizing means being connected to said amplifierdisabling means to render said disabling means ineffective to disablesaid amplifying means when said solenoid is energized, and meansconnected to said solenoid energizing means for controlling theenergizing current delivered to said solenoid and delivering arelatively high initial surge of energizing current and a relatively lowsteady-state holding current to said solenoid.

2. In a dictating machine, means for amplifying electrical voice signalsinput to said machine, an indicator lamp, means for causing said lamp toburn with a relatively high initial intensity when said amplifying meanssupplies no output signal and, when on output signal is supplied by saidamplifying means, to burn with an intensity lower than said initialintensity by an amount dependent upon the magnitude of said outputsignal, a solenoid-operated drive clutch, a switch adapted to connectthe solenoid of said clutch to an electrical energization source,electrical circuit means connected to said switch for short-circuitingthe input terminals of said amplifying means, for disabling saidamplifying means and thereby causing said lamp to burn with said highinitial intensity when said solenoid is not energized, and forpresenting, when said solenoid is energized, an essentially open circuitacross said amplifier input terminals and rendering said amplifyingmeans effective to perform its amplification function, and meansconnected to said switch for controlling the energizing currentdelivered to said solenoid and delivering a relatively high initialsurge of energizing current and a relatively low steady-state holdingcurrent to said solenoid.

3. In a dictating machine, means for amplifying electrical voice signalsinput to said machine, an indicator lamp, means for causing said lamp toburn with a relatively high initial intensity when said amplifying meanssupplies no output signal and, when an output signal is supplied by saidamplifying means, to burn with an intensity lower than said initialintensity by an amount dependent upon the magnitude of said outputsignal, a solenoid-operated drive clutch, a switch adapted to connectthe solenoid of said clutch to an electrical energization source,electrical circuit means connected to said switch for short-circui'tingthe input terminals of said amplifying means, for disabling saidamplifying means and thereby causing said lamp to burn with said highinitial intensity when said solenoid is not energized, and forpresenting, when said solenoid is energized, an essentially open circuitacross said amplifier input terminals and rendering said amplifyingmeans effective to perform its amplification function, and meansconnected to said switch for controlling the energizing currentdelivered to said solenoid and delivering a relatively high initialsurge of energizing current and a relatively low steadystate holdingcurrent to said solenoid, said energizing current control meanscomprising a transistor, a steadystate current-limiting resistorconnected in series with said solenoid and between the emitter and thecollector electrodes of said transistor, said resistor having oneterminal connected to one terminal of said electrical source, saidswitch being connected in series between the other terminal of saidsource and the series combination of said solenoid and said resistor,and a resistance-capacitance network connected to the base electrode ofsaid transistor and adapted to develop an initial transistent signalinput to said transistor when said switch is initially closed, saidtransient signal being adapted to render the emitterconductor path insaid transistor highly conductive for the duration of said transient.

References Cited by the Examiner UNITED STATES PATENTS 3,056,606 10/62Schnueler 179100.2 X 3,099,827 7/63 Wu 179-1001 IRVING L. SRAGOW,Primary Examiner.

BERNARD KONICK, Examiner.

1. IN A DICTATING MACHINE HAVING MEANS FOR AMPLIFYING ELECTRICAL VOICESIGNALS INPUT TO SAID MACHINE, AN INDICATOR LAMP, MEANS FOR CAUSING SAIDLAMP TO BURN WITH A RELATIVELY HIGH INITIAL INTENSITY WHEN SAIDAMPLIFYING MEANS SUPPLIES NO OUTPUT SIGNAL, AND WHEN AN OUTPUT SIGNAL ISSUPPLIED BY SAID AMPLIFYING MEANS, TO BURN WITH AN INTENSITY LOWER THANSAID INITIAL INTENSITY BY AN AMOUNT DEPENDENT UPON THE MAGNITUDE OF SAIDOUTPUT SIGNAL, A SOLENOID-OPERATED DRIVE CLUTCH, AND MEANS FORENERGIZING THE SOLENOID OF SAID CLUTCH, THE IMPROVEMENT OF MEANS FORDISABLING SAID AMPLIFYING MEANS AND THEREBY CAUSING SAID LAMP TO BURNWITH SAID HIGH INITIAL INTENSITY WHEN SAID SOLENOID IS NOT ENERGIZED,SID SOLENOID ENERGIZING MEANS BEING CONNECTED TO SAID AMPLIFIERDISABLING MEANS TO RENDER SAID DISABLING MEANS INEFFECTIVE TO DISABLESAID AMPLIFYING MEANS WHEN SAID SOLENOID IS ENERGIZED, AND MEANSCONNECTED TO SAID SOLENOID ENERGIZING MEANS FOR CONTROLLING THEENERGIZING CURRENT DELIVERED TO SAID SOLENOID AND DELIVERING ARELATIVELY HIGH INITIAL SURGE OF ENERGIZING CURRENT AND A RELATIVELY LOWSTEADY-STATE HOLDING CURRENT TO SAID SOLENOID.